Power amplifiers (PA) may be used in various applications, such as in broadcast equipment for wireless communication. The broadcast equipment may be contained in base transceiver station (BTS) or user equipment (UE) or other transceiver equipment used for wireless mobile communications, such as in LTE, WiMax, WiFi, CDMA, GSM, EDGE, and UMTS standards.
Power amplifiers ideally would produce output signals that are perfect linear amplifications of the input signals. However, when they are manufactured, power amplifiers often impart distortions upon their output signals due to non-ideal circuitry. In order to reduce such distortions in the output signals, additional circuit components are added to amplifier systems to compensate for nonlinear behavior in the power amplifier. Such additional circuits, however, often consume additional power. Additionally, as required bandwidth increases to support high speed communication applications, such compensation becomes increasingly difficult and expensive.
For example, a typical power amplifier in a BTS may represent a significant portion of the cost and power demand of the BTS, for example, 30% of total power demand and 30% of the cost. A typical power amplifier may have one or more zone of nonlinearity, and the nonlinear behavior of the typical power amplifier may be affected by various factors such as power supply, temperature, gain setting, etc. Nonlinearity in the power amplifier may degrade error vector magnitude (EVM), which is used to quantify the performance of a radio transmitter or receiver, and increase spectral regrowth, which is the spreading of signal bandwidth due to distortions.
The nonlinearity of a power amplifier may be dependent upon ambient factors. That is the nonlinearity is dependent upon the conditions of the power amplifier at the same moment when the power amplification occurs. Additionally, the nonlinearity of a power amplifier may be dependent upon memory effects of the power amplifier. That is the output signal of the power amplifier may contain nonlinear distortions generated in a previous point in time. Distortions due to memory effects of the power amplifier may be difficult to compensate.
Thus, there is a need for improved power amplifiers that compensates for nonlinearity efficiently with low power consumption.